The present invention relates to foamed sandwich objects, such as but not limited to sandwich panels having opposing facers between which a core is disposed, and in particular methods and apparatus for manufacturing such objects.
Insulated structures, for example buildings, containers, truck bodies and trailers, may be constructed utilizing insulated sandwich panels having two major surfaces and four minor side surfaces. The side surfaces are “minor” in that they encompass the panel's shortest dimension, whereas the facers encompass the panel's largest dimensions. The ratio between the largest and the shortest dimensions is such that the panels may be considered generally planar. The facers are formed of solid materials, such as aluminum or other metals, polymers, or wood, that may exhibit flexibility in response to forces in the panel's shortest dimension but rigidity in the plane defined by the other two dimensions. Between the two facers is an insulating foam. The facers are generally strong and stiff as compared to the foam core, which is of lighter weight and lower density than the facers. The foam core provides structural support, e.g. resisting shear stresses and deflection, and it may provide thermal insulation.
Insulated sandwich panels may include various structures in the interior volume between the facers that is otherwise filled by the foam, for example vertical or horizontal support posts or ribs that attach to and extend between the inner and outer facers or that attach to just one of the facers. Electrical conduit lines may run through the panel, and troughs or raceways may be provided in the panel facers, attached to and opening through one of the facers, to provide a path for the conduit lines. Wooden or plastic blocks or other structures may be disposed in the volume, extending between the facers, to provide a structure into which screws or nails may be driven as objects (such as logistics tracks) are attached to the sandwich panel facer before or after assembly. Particularly where a panel is used in the roof of the insulated structure, lighting or other electrical fixtures may be secured in the panel within the volume and extend through a hole made in the facer to receive the fixture. These holes may be provided with tape or weather stripping as a seal between the facer hole and the fixture, or trough, to prevent foam leaks and otherwise seal the panel interior.
Various types of foam may be used to form insulated sandwich panels. In typical two-part insulating foams, two monomers react to form a longer chain polymer, releasing gas in the reaction that becomes trapped in closed cells that, in turn, form the foam structure. The trapped gas has a low thermal conductivity, and thus acts as the insulating agent, while the foam cell walls provide the foam's structural characteristics. The volume ratio of gas to solid cell structure is large.
Polyurethane foams, which are commonly used in insulated sandwich panels, are formed from the combination of a polyol and an isocyanate. The isocyanate is generally consistent among polyurethane foams, the variability of which is attributable primarily to the polyol. The polyol's selection generally determines a given polyurethane foam's in place density, its thermal properties, and the timing or reactivity at which the components react to generate foam and subsequently cure.
In so-called spray foam applications, for example, the polyol is chosen so that when the polyol and the isocyanate come together at a foam sprayer head, the resulting liquid or semi-liquid foam agent has a consistency such that the foam agent clings well to vertical surfaces. The reaction rate is slow enough to allow a user to spray a relatively large area before foaming begins or reaches a point at which foaming interferes with the foam's application to desired surfaces. Typically, a panel to be insulated by spray foam would be initially constructed with one facer, the short-side structures and the internal structures, if any, but without the opposing facer. That is, the panel is open at one of its two major sides. The user then sprays the panel's interior volume. Because of the foaming agent's tendency to cling to the sprayed surface, and the agent's relatively slow reaction rate, the user can adequately fill the panel volume, including irregularly-shaped spaces within the volume, if any, before foaming begins or before enough foam expands to inhibit the spray's effective deposition. The user can then place and secure the opposing facer onto the panel's open major side before the foam expands, thereby enclosing the panel interior volume. The sprayed foam then completely expands or rises and thoroughly fills the panel volume. As should be understood, vent slits or holes may be provided in the short sides or facers as necessary to allow the escape of gases as the foam fills the volume. The vent holes may be covered with gas permeable filter material that allows the escape of air or other gases but that blocks passage (leakage) of foam.
Because it is necessary to expose the entirety of the panel volume in order to apply foam by spraying, spray-foamed panels are opened for foaming at one of the facer sides, rather than at one of the short sides. This means, however, that the omitted facer cannot have mechanical or sealed attachments or engagements to interior structures within the panel that would otherwise require the facer's assembly to such structure prior to foaming. Accordingly, while spray foaming is utilized in insulating panels having relatively simple internal structures, for instance those used in buildings, such methods are often unsuitable for insulating panels having more complicated internal structures, for example those used in vehicles.
It is also known to foam sandwich panels through open-pour methods, in which a panel shell that is enclosed on five sides, but open at one of its major sides (e.g., a vacuum element in a press can secure or hold one of the facers and facilitate temporary removal of the second facer from the shell), is moved on a conveyor relative to a foam dispensing head. The open panel shell can be moved along a conveyor system under an elongated dispensing head that extends across the panel's width so that as the panel moves under the dispensing head, the dispensing head deposits liquid for semi-liquid foam agent into the panel's interior. After passing under the dispensing head, the panel shell can be shuttled into a press mechanism, the bottom facer of the open panel shell being received on a platen of the press. An opposing platen holds the other facer (which the platen had earlier removed), for example by suction, opposite the shell's open major side. The press moves the second platen down onto the shell, so that the removed facer again engages the panel shell sides, thereby enclosing the panel's internal volume. The mixed foam agent's chemistry is such that the foam does not rise to fill the volume before the opposing facer is placed down onto the open shell. The press then applies sufficient force to the platens, in opposition to the outward force that the expanding foam applies as the foam agent exotherms. As should be understood, a combination of aluminum or plastic extrusions and wood or polymer strips or blocks may be placed along the panel edges to construct the short sides and maintain the foam within the side surfaces. The press mechanism generally does not provide platens to apply resistive pressure to the side surfaces. Rather, the pressure applied by the major-side platens compresses or pinches, without crushing, the side members between the facers, holding them in place sufficiently to resist the foam's outward pressure. Again, vents may be provided in the side members to allow air and other gases to escape as foam fills the panel volume, and semi-permeable filter material may be placed over the vents to block the interior foam's escape.
As with spray foaming methods, open pour methods require a facer's removal, thus precluding use with foam panels that have internal structures that would require attachment prior to foaming.
It is also known to pre-form insulation foam into blocks, cut the block foam into desired shapes to fit a panel interior, and then secure the one or more resulting foam pieces into the panel. This procedure can accommodate complicated interior panel volumes but tends to limit a panel's thermal performance. When a foam agent is allowed to react and foam within an enclosed volume, and when there is sufficient foam agent such that the resulting foam fills the volume and exerts pressure against its sides, the restricted enclosure increases foam density and tends to promote a more uniform cell structure. This, in turn, generally improves the foam's thermal characteristics. Block-formed foam, however, is formed within a structure that may be bounded on some, but not all, sides, thereby allowing the foam to rise freely, with the foam's weight being its primary restriction. This results in a cell density lower than, and a cell structure more irregular than, foam that is formed in a confined volume. Even if the foam to be cut is formed in a completely enclosed cavity, the subsequent cutting operation allows cell gases to escape and degrades the ability of the cut blocks to insulate effectively. Heavy or high density Styrofoam, for example, may have a density in the range of 2.1-2.5 pounds per cubic foot. Furthermore, block urethane foam tends to shrink for some period after initial curing. Thus, block-formed urethane foam cannot be used immediately after its formation and must be allowed to rest for some intervening period of time. During this time, however, the foam can experience some degree of loss of foam cell gas (outgassing), further impairing the foam's thermal performance. Finally, while block foam may be cut to closely fit a panel's internal structure, the fit is not as close as that resulting from foam that is initially inserted into the panel as a pre-expanded or foamed liquid and allowed to rise to fill and fill the panel's interior. While adhesives may be used to fill gaps around, and otherwise secure, block foam within a panel, the adhesive generally has a lower thermal performance than the foam and adds weight and cost. The formation of sandwich panels using block foam can also be labor intensive.
Where an insulated sandwich panel includes interior structure that interacts with the facers or external elements that attach to or through the facers, it is known to insert the foam by injection of pre-foam or semi-foamed liquid into an enclosed panel volume. The sandwich panel shell is generally first constructed so that the two facers and the separating side members completely enclose the panel's interior volume and, therefore, the panel's interior structures. One or more holes is drilled or otherwise formed in one or both facers and/or a side member. A user places a foam injection nozzle at a hole and injects liquid or semi liquid (froth) foam agent into the enclosure. One such hole may be sufficient for a small panel, but larger panels may require multiple interior enclosures or segments, sometimes referred to as cavities, and corresponding foam access holes. Accordingly, it is known to divide a panel's interior volume into discrete segments or cavities that are sealed from each other with respect to the foam. Respective holes are drilled to each segment through the side members to provide for foam dispensing and escape of gases from the segment interior. The panel shell is then placed into a press having opposing platens that abut the facers and possibly including a fixed position perimeter board or mold board abutting and supporting the short sides to resist the forces resulting from the core material's expansion. The platens apply opposing pressure to the facers, again pinching the side members to hold them in place. The access holes are typically along one of the panel's sides, and the panel is generally installed in the press so that this side faces upward, or at least oriented such that this side is exposed to an operator working at the press. The foam nozzle is disposed proximate the panel edge on a moveable structure at the press by a counterbalance so that the operator may deploy the nozzle and move the dispensing head and nozzle down the panel's length, sequentially engaging the foam nozzle at the panel shell's access holes to thereby fill the panel's volume.
At the time the panel's layout is designed, the volume of each interior segment can be determined. This information, and the sequence in which the individual segments will be filled, may be provided to a computer that controls the foam machine's operation. The foam machine computer may also be programmed with or has access to the amount of foam agent needed per unit volume in order to result in foam (within a given volume) having the density and cell formation desired for a given panel. Alternatively, all of these calculations can be made outside of the computer programming, so that the computer (including a corresponding database) receives information describing only the number and sequence of foam agent injections to be made for a given panel and the respective amounts of foam agent to be provided in each of the injections.
When the panel shell is placed in the press, an operator initiates the foaming sequence. The operator actuates the press controls to direct the press platens to apply pressure to the opposing shell facers and actuates the foam machine computer to assume the beginning of the injection sequence. For the latter step, the operator places the foam injection nozzle at the access hole for the first volume segment in the sequence (the first hole, at one end of the panel edge) and actuates the trigger. This causes a signal to be received at the foam machine computer, and the computer correspondingly controls fluid valves and pumps from the polyol and isocyanate sources to deliver respective amounts of those substances to the foaming head so that the foaming head mixes and dispenses the predetermined amount of foam agent into the first segment. After the amount of foam agent has been dispensed, the operator removes the dispensing head from the first access hole, moves the dispensing head to the second hole in the sequence, engages the second access hole, and actuates the trigger. This causes the foam machine computer to control the system to deliver the amount of foam agent corresponding to the second volume segment. Generally a second operator follows the first operator, plugging the holes after the liquid foam agent has been deposited into the respective volume segment. This process repeats until corresponding foam agent amounts have been injected into all the panel's interior volume segments.
As noted, the press platens apply pressure to the facers as the operator injects liquid foam agent into panel shell interior. Supports may be provided in the panel interior to provide structure and/or prevent the shell's deformation into the volume. As the foam agent exotherms, i.e., as the foam expands or rises, pressure and temperature build within the panel shell interior. As should be understood in this art, it is desirable to maintain the panel system at a relatively constant temperature range during foaming, and for this purpose the press platens may be provided with a series of fluid paths within each platen. When the platens close upon the non-foamed panel shell, fluid, heated to a pre-determined temperature that is desirable for the foaming process, for example, 110° F., circulates through the platens, warming the facers to approximately the same temperature. As the foam exotherms, however, and as the temperature within the panel rises, the fluid flowing through the platens becomes a cooling agent, carrying heat away from the platens to the temperature control system, which now cools the water to 110° F. The temperature regulation of foam insulated sandwich panels should be well understood in this art. Such procedures may be used with the embodiments of the present invention discussed herein but are not, in and of themselves, part of the present invention and are, therefore not discussed in further detail herein.
As with panels made by a spray foaming and open pour methods, vent holes may be provided in the panel shell facers or sides, with suitable filter material, to allow escape of gases during foam expansion while retaining foam within the panel interior.
Once the foam has risen, and thereby completely filled the panel interior volume, the panel remains in the press for a period of time sufficient to allow the foam to cure. As should be understood in the art, curing is the process by which the foam cross links and the cell structure solidifies into its final form.
As noted, the press is operated in such a way as to maintain the panel at a desired temperature range, for example 110° nominal, or within a range of about 105°-115°. As the facers' temperature increases during initial warming, and, to a lesser extent as the foam agent exotherms and the foam cures, the facer material slightly expands. To avoid wrinkles and other possible deformities in the facer surface, the facers and side members are sealed against each other using a foam tape (e.g. as used in or as common weather-stripping material) that allows some degree of slip or relative movement between these components.
As noted, the opposing pressure from the press, pushing the two facers toward each other and against the side members, holds the facers and the side members to each other during the foam injection and curing process. The foam, in turn, holds these panel surfaces together with the core in the finished panel. In some instances, however, the side members are not intended to be a part of the finished sandwich panel, and the side members can be removed after the panel is removed from the press. This can be accomplished by trimming the post-cured panel or by using side members coated to prevent the foam's adhesion to the side members, thereby facilitating their removal.
Various types of presses can be utilized for enclosed injection foaming Referring, for example, to FIG. 1, a mandrel press 10 comprises a three-sided press having a cantilevered inner portion 12 upon which three inner platens 14 are disposed. Opposite inner portion 12 are two outer clamshell portions 16, each having one side platen 18 and a top platen half 20. Press 10 is designed for use in manufacturing insulated panels which are a part of insulated semi-trailers. Prior to injecting the foam insulation, the panel shells for the trailer's sides and roof are constructed and assembled onto a semi-trailer chassis. As described above, the panel shells comprise opposing facers with side members extending around the panel edges to thereby completely enclose the panel shell interior volume. Each panel may be a continuous structure extending the entire length of the trailer, or the trailer may be formed by connecting multiple discrete panel segments in each of the two sides and the roof. Regardless of such arrangement, each panel shell has interior structures, and each panel's interior volume is generally divided into discrete segments. Each side panel has a top rail portion and a bottom rail portion, whereas the roof panel has top rail portions on each longitudinal side. The side panel top rail portions connect to the roof panel top rail portions to secure the panels together. Access holes are drilled in the top rail portions of the side panels in communication with respective interior volume segments so that the holes are accessible from the top of the trailer when the trailer body is assembled. Access holes to the roof panel interior volume segments are also drilled into one of the top rail portions, but these holes are accessible from the side of the roof panel when the panels are assembled onto the trailer chassis. Once the panels are assembled onto the chassis, the nearly-formed trailer (the trailer's rear frame and doors are not yet assembled) is backed up to press 10 while side structures 16 are pivoted outward, as shown in FIG. 1. The trailer's rear opening is backed up to and over central cantilevered press portion 12 so that press portion 12 extends into the trailer's interior and so that respective platens 14 face the trailer's side panels and roof panel. Clamshell side press portions 16 are then pivoted inward toward the trailer so that the top edges of the side portions meet. Central portion 12 is expanded and side platens 18 contracted to oppose the outer portion of the trailer side panels, and ultimately platen surface 20 oppose the outer portion of the roof panel. The inner and outer platens apply pressure to their respective panel surfaces. Press 10 includes a series of holes that align with the access holes in the panels. An operator may then insert a foam head nozzle through the holes in the press, engage a corresponding access hole in one of the panel shells, and begin injection of foam agent into a corresponding panel interior volume segment. Once the foam has been deposited, expands, and cures, outer portions 16 are opened, the trailer shell is removed from the press, and the trailer's construction is completed.
It is also known to manufacture the panels individually, prior to their installation in a trailer. Referring to FIG. 2, for example, a press 22 includes two individual press portions 24 on each side of a central frame. Each press portion 24 includes an inner platen 26 and outer platen 28 that can be pivoted toward and away from platen 26 by actuation of a series of hydraulic pistons 30. A panel shell constructed as discussed above is inserted between platens 26 and 28. Cylinders 30 close platen 28 onto the panel shell so that the panel shell is held securely between the two platens, and pressure is applied. The holes in one of the panel's side members, which provide access to the panel's interior volume segments, are on the side of the press facing upward and are thereby accessible to a user operating the foam injection nozzle from a catwalk above the platens in the central frame.
It is also known to arrange a press so that the platens are disposed horizontally. The assembled panel shell is inserted into the press between the platens so that the facers are also aligned horizontally against the respective platens and so that the side edge in which the access holes are defined is vertically aligned. The foam agent is therefore injected into the respective spaces in a horizontal direction. One example of a horizontally oriented press is U.S. Pat. No. 5,722,276, the entire disclosure of which is incorporated by reference herein.
Referring to FIG. 3, a six-sided polyhedron panel shell 30 for use in a press system for injecting insulating foam into individual interior shell volume segments includes an aluminum outer facer 32 in the form of a relatively thin, planar sheet. The side of aluminum facer 32 facing inward to the panel's interior volume is first covered with an epoxy, polyester or a similar coating to facilitate foam adherence to the facer, as should be understood. A series of extrusion and strips or blocks 34 are disposed along the four edges of aluminum facer 32 and extend upward therefrom for a short distance (compared to the panel's longitudinal dimension) to form the panel's side members. These side members may be made of any desirable material, for example aluminum, wood or various plastics including plastic foams such as Styrofoam. A series of foam tape segments or adhesives 36 are disposed along both rims of the side members in order to adhere the side members to the aluminum facer and to a polymer laminate inner facer 37 (FIG. 4). As the illustrated panel shell 30 is to be used to form a trailer side panel, an aluminum top rail and aluminum bottom rail are attached to the panel's longitudinal edges. For example, a bottom rail 38 is attached to the side members 34 by a series of rivets 40, adhesive or other suitable means.
Side members 34 enclose a volume 42 adjacent the interior surface of facer 32. Within that volume, a series of elongated reinforcing ribs 44 extends across the interior surface of facer 32 between the top and bottom longitudinal side members 34. Ribs 44 attach to facer 32 and provide structural support thereto. As should be understood, such supports in a non-insulated trailer panel would typically extend entirely between the inner and outer facers and attach to both. In this insulated panel, however, it is desirable to maximize the foam's continuity to thereby optimize the panel's thermal characteristics, and lower profile ribs 44 are used instead of fully-extending posts. It should also be understood, however, that J-shaped and Z-shaped posts may also be used in insulated panels, extending entirely between the two facers.
A series of wooden or polymer blocks 46 may be disposed adjacent respective ribs 44 and abut the bottom longitudinal side member 34, just above bottom rail 38, so that blocks 46 extend in a row along the bottom of the panel shell. Upon installation of the inner liner facer, which will abut blocks 46, the blocks provide a backing surface so that a scuff band may be disposed on the side of the inner facer opposite the blocks, and may be secured to the panel at that position by screws extending through the scuff band, the inner facer, and into blocks 46 or alternatively through blocks 46 and into ribs 44. A similar row of blocks are also attached to ribs 44 and extend in a line parallel to the longitudinal side members 34 and extending through the middle of the panel. A similar row of blocks 50 extend longitudinally through the panel near the panel top. The polymer inner liner facer also abuts these blocks, which provide support for the attachment of longitudinal logistics tracks that extend along the panel's length on the inner side. Referring also to FIG. 4, an aluminum support plate 52 extends along the panel's upper longitudinal side member 34, within the interior volume of the panel, from the panel's back side edge 34 toward, but stopping short of, its front side edge 34. Plate 52 provides support for a sliding track for subsequent attachment to permit installation of an overhead or garage type rear door that will be disposed within the trailer interior and attached to the panel through the inner facer. An aluminum top rail portion 54 is disposed at the top of the panel and attaches to aluminum facer 32.
Also attached to some of the ribs 44 intermittently along the panel's longitudinal length are a plurality of PVC plastic foam dams 55. In this instance, a foam dam 55 is attached to every third support rib 44. As can be seen in FIG. 3, the base of each foam dam has a cut out for each block 48 and 52 in its path and slightly overlaps an end of a block 46. As can be seen in FIG. 5, foam dams 54 all slope toward the same one of the panel's two vertical edges 34 or side members.
As can be seen in FIGS. 3 and 5, a series of holes 56 is drilled through bottom rail 38 and the longitudinal side member 34 behind it communicating with respective inner volume segments 58 defined between adjacent foam dams 55 or between a foam dam 55 and an opposing vertical side member 34. When the polymer inner facer is applied to the panel shell's open major side, such that the laminate polymer facer abuts the tops of blocks 46, 48, and 50, the inner facer also abuts the distal edges of foam dams 55, even with their slope or bend.
A combination of (possibly double sided) foam tape 36 and adhesive initially holds the inner facer and outer facer onto the side members, thereby holding the panel shell together. Clamps placed along the bottom edge of the now-assembled panel shell are attached to carrying lines of a bridge crane disposed along the ceiling of a manufacturing facility. The bridge crane pulls the panel upward so that it is suspended vertically, upside down, with bottom rail 38 oriented upward. The crane conveys the suspended panel shell to a press, such as an A-frame or book-type press 24 in FIG. 2, and disposes the assembled shell between the press platens. The press closes, as described above, and an operator injects foam agent into the respective volume sections 58 sequentially as described above. The first section 58 to be injected with foam is indicated at 58A in FIG. 3, followed sequentially by 58B, 58C, and 58D. As each volume segment fills with foam, the foam pushes a sloped or bent foam dam 55 toward the still-unfoamed adjacent section 58. This further pushes or forces the foam dam against the inner polymer liner facer, strengthening the seal between the panel and the dam. Blocks 48 and 50 laterally support the dam, preventing the dam from pushing over center, further toward the adjacent open volume section, and thereby comprising the foam seal between adjacent sections. The foam dam is unnecessary at the lower end of the panel, due to the presence of blocks 46, but it should be understood that where no blocks 46 are used, the foam dams, if employed, would extend to the panel bottom.
Accordingly, foam dams 55 and blocks 46 seal adjacent volume segments 58 from each other, so that foam expanding in one segment or cavity 58 doesn't leak into an adjacent segment in which foam has not yet expanded. If a foam dam does not properly seal between adjacent volume segments, or if any other leaks occur therebetween, expanding foam in the segment in which foam is rising can leak or inject under substantial pressure (above atmospheric pressure) into the adjacent volume segment, in which the foam has not yet risen. The leaked foam, being injected into the adjacent volume segment under higher than atmospheric pressure and without spatial restriction, tends to have irregular, elongated cell structures, and is partially stripped of contained cell gases, resulting in excessive density. The resulting leaked foam has correspondingly poor thermal characteristics. When foam in the volume segment into which foam from the adjacent segment has leaked then rises up and around the leaked foam to fill the volume space, and the leaked foam forms a sub-volume of poor thermal performance within the volume segment. To prevent such leaks, therefore, foam dams must be carefully installed, and the dams and other partition materials between volume segments must be carefully constructed and arranged.